The invention relates to bags that are reclosable by means of closure strips, and to the manufacture thereof.
Methods are known for manufacturing bags out of plastics material in which each bag opening has two closure strips and a cursor that slides thereon. During manufacture, the cursor is situated at a predetermined distance from the ends of the strips so as to avoid interfering with the heat-sealing and cutting operations that are performed. However, when the bags are placed one on another, the cursors pile up against one another, thereby generating a stack whose height is much greater at the cursors than over the remainder of the bags. Thus, storage of the bags is complicated by the volume of such stacks and by their instability. In particular, it is difficult to make up rolls or stacks having a large number of bags.
Document U.S. Pat. No. 5,682,730 discloses a stack of bags having a lower series of successive bags in which said distance has a first constant value such that the cursors are stacked one on another close to one end of the strips, and an upper series of successive bags in which said distance has a second constant value, different from the first value, with the cursors of said second series being stacked one on another at the other end of the strips. In this way, the two stacks of cursors do not interfere with each other and both of them occupy almost the same height, thereby greatly reducing the total height of the stack. That disposition is made possible because the bags are flexible. Nevertheless, the height of the stack of bags remains relatively large.
An object of the invention is to improve storage of bags, in particular for the purpose of making rolls or stacks of very large numbers of bags.
According to the invention, this object is achieved by a set of at least three consecutive bags in a succession, each bag having two closure strips and a cursor situated at a respective distance from one end of the strips, the strips and the cursor being identical between the bags, and in which, between the bags in each pair of adjacent bags, the said distances are different.
Thus, a disposition of the cursors is obtained which differs from the above-mentioned known disposition and which makes it possible to store the bags in a volume that is different and more stable, and for example in a stack that is of smaller height. For example, the cursors can be relatively offset by half the length of a cursor. Under such circumstances, stacking the bags causes the strips to be twisted slightly, and causes the cursors that lie one on another to be inclined. This reduces the volume of the stack at the cursors.
Preferably, the said distances differ by not less than the size of the cursors parallel to the strips.
In this way, the bags can be stacked one on another with the strips being contiguous but without the stacked cursors interfering with one another, the cursors being disposed next to one another. Under such circumstances, the volume of the set of bags corresponds substantially to that generated by the walls and the strips, and is therefore considerably reduced. As a result, the stack of bags is stable.
Advantageously, the said distances on adjacent bags vary in a monotonic progression.
It is thus possible to stack a very large number of bags while optimizing the volume available for the cursors without risking interference, even between cursors of bags that are not consecutive.
Advantageously, the said distances vary by an increment that is constant.
Advantageously, the bags are disposed so that their strips are contiguous.
Advantageously, the set constitutes a roll of bags.
Advantageously, the set constitutes a stack of bags.
The invention also provides a method of manufacturing at least three bags each having two closure strips and a cursor, the strips and the cursors being identical between the bags, in which each cursor is disposed at a respective distance from one end of the strips, and in which the cursors are disposed in such a manner that the said distances are different between any two successive bags.
The invention also provides an installation for manufacturing bags each including two closure strips and a cursor, the installation comprising means for placing each cursor at a respective distance from one end of the strips, in which the means are organized to place the cursors of any two successive bags at distances that are different.